Forums are designed around a certain subject or topic. Companies will create a forum for one of their products. For example, Ford has several forums about a car or truck. The forum is split into sections and in the sections are different topics. On a forum you need to post in the correct section and topic, otherwise, they will remove your post.
In a forum, each new post that is created is called a thread. A thread can either be a question, a poll about a certain topic, or a rather long detailed description about how to build or fix something. In a forum, you can upload images to help you describe your topic or show a problem.
The forum is an active discussion group. Where the members can comment on the forum thread. A comment is called a post in a forum. In the forum, you have the option to tag a person by @Admin or you can quote a person when you hit the replay button.
As a forum member, you don't need to be an expert to join the forum. You can go to a forum looking for help or even as an expert to answer and help others.
On a Q & A site, it is designed so a person can post any type of question they want. They can ask people about their homework, problems in a relationship, ideas about opening a business and the list goes on and on. Questions are asked randomly and normally the experts in the community will answer the question for a person. In a questions and answers site, it might take a bit of research to find the answer for the person. Where forums are topic related and they don't allow posting of just any question on the forum. The question or new thread has to relate to the forum.
In reality, the two sites are very similar, with one exception. On a forum it isn't possible to post just anything on the forum You have to stay on topic and stick with what the forum is about. On question and answer sites most sites will hire experts to answer the question. Where on a forum anyone can answer the question. Forums also use a certain type of software normally known as a PHP script that can record stats, who is online and how many different threads and answers are in each topic. They can also show how many people have viewed each topic. Where on most Q & A sites they can't do this. Furthermore, most companies will create a forum to help their customers. This can help the company cut down on the number of calls they receive in their call center.